Search PubMed⌕ Search

Biomedical subjects

J C Hansen

Publications and source records attributed to J C Hansen.

At least 145 records · Page 8Linked to original sources
PubMed1983

Human exposure to heavy metals in East Greenland. II. Lead.

The concentration of lead in 175 blood samples originating from the district of Angmagssalik, East Greenland and 130 from Aarhus, Denmark, has been determined. Both Greenland and Danish males had significantly higher (5%) blood lead than females (Eskimoan males 14.8 micrograms Pb/100 ml, females 12.8 micrograms Pb/100 ml; Danish males 10.5 micrograms Pb/100 ml, females 7.7 micrograms Pb/100 ml). For Danes living temporarily in Greenland the values were: males 10.5 and females 10.2 micrograms Pb/100 ml. Eskimos of both sexes were found to have higher blood lead values than Danes living in the same area. Danish males from Greenland and Denmark were not found to be different, whereas Danish women living in Greenland had a significantly higher (5%) mean value than women living in Denmark. In the Eskimo group, but not in the Danish, a weak, positive, but significant age correlation was found. 4 samples of Eskimo origin exceeded 35 micrograms Pb/100 ml accepted in the EEC as a maximum value for non-occupationally exposed persons. When re-examined 5 months later, all values were below this limit. The influence of eating habits (local or imported food) and smoking habits was tested, but not found to influence the blood lead concentration. The results have confirmed that blood lead levels in Greenland are comparable to those found in European industrialized areas. The reason for the unexpected high level in the arctic area with minimum car driving and industry remains to be clarified.

Adolescent↗
PubMed1983

Separation of overlapping waveforms having known temporal distributions.

A simple Fourier technique is described that allows isolation of component waveforms from recordings of time-shifted, overlapping, linear sums of these components. This procedure can be applied if certain assumptions are satisfied, namely, the times of occurrences of the underlying component waveforms are known, the component waveforms are time-invariant, and there are at least as many different recordings as there are underlying component waveforms. The method is a type of adaptive inverse filtering, and can be generalized to allow recovery of waveforms that have been distorted by many time-invariant linear processes in addition to time delays. An application of the technique to human scalp-recorded event-related potentials (ERPs) is discussed which allows resolution of overlapping stimulus-locked and response-locked waveform complexes. Some possible effects of violating the assumptions of the procedure are explored for this example. The method should prove of value when it is impossible to record the underlying component waveforms in isolation, and the waveshapes, rather than their times of occurrence, are important experimental dependent variables.

Brain↗
PubMed1983

Selective attention to multidimensional auditory stimuli.

Event-related brain potentials (ERPs) elicited by multidimensional auditory stimuli were recorded from the scalp in a selective-attention task. Subjects listened to tone pips varying orthogonally between two levels each of pitch, location, and duration and responded to longer duration target stimuli having specific values of pitch and location. The discriminability of the pitch and location attributes was varied between groups. By examining the ERPs to tones that shared pitch and/or locational cues with the designated target, we inferred interrelationships among the processing of these attributes. In all groups, stimuli that failed to match the target tone in an easily discriminable cue elicited only transitory ERP signs of selective processing. Tones sharing the "easy" but not the "hard" cue with the target elicited ERPs that indicated more extensive processing, but not as extensive as stimuli sharing both cues. In addition, reaction times and ERP latencies to the designated targets were not influenced by variations in the discriminability of pitch and location. This pattern of results is consistent with parallel, self-terminating models and holistic models of processing and contradicts models specifying either serial or exhaustive parallel processing of these dimensions. Both the parallel, self-terminating models and the holistic models provide a generalized mechanism for hierarchical stimulus selections that achieve an economy of processing, an underlying goal of classic, multiple-stage theories of selective attention.

Acoustic Stimulation↗
PubMed1981

The influence of selenium on mercury distribution in mice after exposure to low dose Hg0 vapours.

The influence of selenium administration on retention, elimination and organ distribution of mercury was studied in female mice exposed to 30 or 80 micrograms m -3 mercury vapour. The results demonstrated that, as after low doses of mercuric mercury, only excess selenium reduced the elimination of retained mercury vapour from the whole body. However, selenium was able to influence the organ distribution of mercury, even when the whole body burden of mercury was not affected. In mice, contrary to rats, selenium increased the lung and kidney concentrations of mercury without affecting its concentration in the liver.

Animals↗
PubMed1981

Mercury/selenium interaction. A comparative study on pigs.

A pilot experiment carried out on three pigs have confirmed that interaction between inorganic mercury (203HgCl2) and selenium (Na275SeO3) after single intraperitoneal injections are qualitatively uniform in mice and pigs. The detoxifying effect of selenium on mercury toxicity seems to be due to a formation of a biologically inactive complex containing the elements in an equimolar ratio. The complex is unable to pass biological barriers, placenta and choroid plexus and is stored in the liver and the spleen.

Animals↗
PubMed1980

On the influence of zinc on mercury/selenium interaction.

Pretreatment with zinc does not change the wholebody retention and elimination of mercury, either when mercury is given alone, or when mercury and selenium are given simultaneously in single doses. Distributional effects are observed, however, as higher retention levels of mercury are seen in kidneys, liver and spleen after pretreatment with zinc. The clearance rate of both elements remains unaffected, indicating that zinc does not truly interact with mercury and selenium. The zinc effect is probably due to a higher initial retention of mercury, especially in the kidneys.

Animals↗
PubMed1980

Endogenous brain potentials associated with selective auditory attention.

In a selective attention experiment, event-related potentials (ERPs) were recorded from 12 subjects who listened to sequences of high and low frequency tone pips, presented binaurally in random order at a rapid rate. Their task was to attend selectively to either the high or low frequency tones and to press a button upon detection of occasional longer-duration tones at the appropriate frequency. The effect of attention was manifest in difference wave forms obtained by subtracting ERPs to the shorter tones when they were unattended from their ERPs to the same stimuli when they were attended. The difference waves consisted of a broad, multiphasic negative component (Nd) with its later phase (300-400 msec) being more frontally distributed on the scalp than either its early phase (100-300 msec) or the N1 component that was evoked in a reading condition. The amplitude and latency of onset of Nd varied systematically as a function of the frequency separation between the tones. It was concluded that the effect of selective auditory attention on the N1 component (ca. 100 msec latency) is not due solely to an enlargement of the exogenous N1 component of the vertex potential, but rather includes the addition of a prolonged endogenous component. A simple gating mechanism for human selective attention was thus rejected.

Adult↗
PubMed1979

Wholebody elimination of 75SeO2-3 and 203HgCl2 administered separately and simultaneously to mice.

A study of wholebody elimination of mercury (203HgCl2) and selenium (75SeO2-3) given separately or simultaneously in single doses by intraperitoneal injections to mice has been performed. The conclusion of this study can be summarized as follows: there seems to exist a homeostatic mechanism for selenium, but not for mercury; increased retention is observed for both elements when administered simultaneously. Maximum retention of 1 element is observed, when the other is given in excess or equimolar ratio to the other. Excess mercury provokes a pattern of selenium retention similar to that found in case of selenium deficiency. The wholebody molar ratio of mercury and selenium tends towards 1. When this happens, mercury as well as selenium are eliminated at a rate different from what is seen when the elements are administered separately. Selenium therefore seems to play a direct role in metabolism of inorganic mercury.

Animals↗
PubMed1979

The kinetics of 75Se-selenium in relation to dose and mode of administration to mice.

To investigate the effect of selenium in relation to different environmental conditions a study on the kinetics of the element in mice has been carried out on 54 female mice. 75Se (selenite) was administered as a single dose or continuously through drinking water. Different dosage levels were used ranging from "tracer dose" to subtoxic doses. Wholebody counts revealed a biphasic elimination. The first rapid phase was strongly dose-dependent, while the slower second phase of elimination appeared independent of dose as well as mode of administration with a biological half-life of 14.4 +/- 3.2 days. Liver, blood, kidney and lungs were found to contain most of the selenium, here also a two-phased elimination was observed. The biological half-lives for elimination calculated during the second phase gave a mean of 10.7 days with a range of 8.7 to 12.5 days. With continuous administration through drinking water a steady state was obtained after 300 to 400 hours of administration according to concentration. A linearity between amount retained at steady state and log concentration in drinking water is indicated. The results on biological half-lives are discussed in relation to previous publications.

Administration, Oral↗
PubMed1978

Risk of infection from heavily contaminated air.

In a factory processing shea nuts the dust concentrations were found to be up to 145 mg/m3 [80% respirable (1--5 micrometer)]. Bacterial examination of the dust revealed that under the worst conditions observed a worker might inhale 350,000 bacteria per 8 h. Of these, 3,000 were Ps. aeruginosa and 1,500 Salmonella spp. of nine different types. The possible health effects of these findings are discussed.

Air Microbiology↗
PubMed1978

On arginine splitting as a taxonomic criterion with special regard to the separation of Aeromonas and Vibrio.

An investigation of various methods and media intended for arginine testing of Aeromonas or Vibrio, showed that the method of Thornley (1960) was superior to the others for this purpose because it showed the best conformity with the established taxonomy of a number of type strains and because it furthermore yielded the lowest percentage of false positive reactions from a number of Aeromonas/Vibrio-suspect strains of marine origin.

Aeromonas↗